Middle-Late Jurassic persilicic volcanic rocks in Haimosaige area of Inner Mongolia constitute one of the most important part of Mesozoic volcanic rocks in the Da Hinggan Mountains. In this paper, the authors studied the ages and geochemical characteristics of the rocks so as to probe into their tectonic settings. The test and analysis were completed at Tianjin Institute of Geology and Mineral Resources. The zircon U-Pb dating by LA-MC-ICP-MS technique indicates that the crystallization ages of the volcanic rocks vary from 164.0±1.0 Ma to 155.5±0.9 Ma, suggesting middle-Late Jurassic. Geochemical researches indicate that the volcanic rocks from Haimosaige area are rich in silica (SiO₂=62.09%～77.57%), alkali (K₂O＋Na₂O=7.27%～10.13%), K(K₂O/Na₂O=1.10～2.82) and poor in calcium (CaO=0.16%～2.46%, 0.73% on average), magnesium (MgO=0.10%～1.08%, 0.29% on average, Mg^#<45) and have high FeO^T/MgO ratios (FeO^T/MgO=2.37～7.22, 4.49 on average), implying a typical high-K calc-alkaline to shoshonitic series with metaluminous and peraluminous features (A/CNK=0.98～2.29). The rocks are poor in rare earth elements with ∑REE being 137.6×10^-6～315.3×10^-6, enriched in LREE , LILEs (Rb, Ba, Th, K) and depleted in HFSE, especially Nb, Ta, Sr, P and Ti. The δEu values vary from 0.14 to 1.54 (0.51 on average), with most rocks having moderate negative Eu anomalies. Similar REE distribution patterns imply that the volcanic rocks came from the same magma source. Most of the volcanic rocks with the characteristics of post-collision granites have lower Sr (Sr=46.2×10^-6～799.3×10^-6, 208.0×10^-6 on average), high Yb (Yb=2.02×10^-6～4.23×10^-6) and obvious geochemical correlation. In combination with previous studies, the authors hold that the rhyolitic magma, which was in a post-orogenic extensional setting, was formed by varying degrees of the crust partial melting and the residua had a little plagioclase and hornblende. It was probably associated with the strike-slip and extension caused by the oblique subduction of the Palaeo-Pacific Ocena. These conclusions have most important significance for studying the volcanic activities and tectonic settings of Middle-Late Jurassic volcanic rocks. 164.0±1.0～155.5±0.9 Ma might indicate the transform from orogenic to post-orogenic extensional setting between Middle-Late Jurassic and Early Cretaceous. The results obtained by the authors impose new constraints on tectonic-magmatic evolution of the Da Hinggan Mountains in Middle-Late Jurassic and also provide basic information for further research.